Metal powder purification



May 1, 1962 M. RICHELSEN METAL POWDER PURIFICATION Filed Oct. 30, 1958 INVENTOR. 777m'Z .fl'ce-Zis'ei? United States Patent 3,032,409 METAL POWDER PURIFICATION Mark Richelsen, 400 Prospect Ave., Medina, N.Y.

- Filed Oct. 30, 1958, Ser. No. 770,660

Claims. (Cl. 75.5)

This inventionvrelates to the purification of metal powder and is particularly concerned with the recovery of and removal of organic impurities from the metal powders produced in metal grinding operations using grinding fluids or coolants.

Metal grinding operationsresult in the production of large quantities of fine metal powders which in most cases are contaminated with the oils, soaps, detergents, etc., present in the grinding fluid employed to prevent excessive heating of the work and the grinding wheel. Removal of such contaminants by washing withsolvents has proved to be impractical commercially since, because of the extremely high surface area of the'very small metal particles, excessive amounts of solvent are required and in many cases the contaminants are redeposited on Further, in some cases the metal particles.

the particles. are magnetically charged and tend to flocculate, thus interfering with solvent extraction of the oils, etc. present.

The use of detergents in washing the metal particles free of the contaminants is also not commercially feasible since the grinding fluids already contain surfactants that may be incompatible. There may also be adsorption of the added detergent on the metal particles. Further, because of the fineness of the metal particles, filtration for removal of the wash liquor or. the solvent, when solvent extraction is employed, is very diflicult.

It is, therefore, an object of the present invention to provide a method for effectively removing organic contaminants from metal powders.

More specifically, it is an object of the invention to providea method of thecharacter described which does not involve solvents or other liquids.

Another object of the invention is to provide a method of the character described which may be inexpensively carried out.

A further object of the invention is to provide novel apparatus suitable for carrying out the removal of organic contaminants from metal powders.

Other objects of the invention and its advantages will be apparent from the following specification thereof taken in conjunction with the drawing which illustrates a preferred embodiment of apparatus for carrying out the novel method referred to.

It has been discovered that contaminating organic materials such as oils, surfactants and the like may be effectively removed from metal powders by a distillation process in which care is taken to prevent aggregation of the metal particles. The process is preferably performed in two stages. In the first stage the metal particles are dispersed while being heated in a current of hot. gas. In the second stage the particles are mechanically agitated while being heated in a still or retort. Convenient means for carrying out this two-stage process is shown in the drawing and described below.

. In the drawing the numeral 1 refers to a screw conveyor driven by suitable means (not shown) adapted to supply contaminated metal powder from a suitable source '(not shown) to the feed tube 2 that leads into the upper end of a heating column 3. The metal particles are dis- 3,932,489 Patented May 1, 1862 persed by the grid 6 and fall through column 3 in dispersed condition countercurrent to hot gases introduced into the column near the bottom, thereof through a pipe or flue 4. i The end of the flue 4 preferably extends into the heating column 3 and is provided with a baffle 5 for spreading out the stream of hot gases. The lower end of the column 3 serves as a collector in which the metal powder heated by the gases from the flue 4 is received and this end is in communication with another screw conveyor 8. Although not so illustrated to avoid excessive drawing detail, the heating column 3 is preferably insulated in any suitable way to prevent loss of heat from the metal powder therein.

The conveyor 8 is driven from any suitable power source (not shown) by the'belt 9 and pulley 10 on the end of the shaft 11 that extends outwardly through the packing gland 12. The screw 13 of the'conveyor 8 feeds the heated metal powder from the bottom of the heating column 3 through the tube 14 into a rotating still or retort designated generally by the numeral 17.

The still 17 comprises a horizontally disposed .tube 18 having at the end adjacent to the conveyor 8 a tubular extension 19 that receives the tube 14 of the conveyor and is rotatably supported in a bearing 20. The outer end of the extension 19 is sealed by a gland'21. At its other end, the tube 18 is closed and provided with a concentric shaft 22 rotatably supported in a bearing 23. Rotation of the tube 18 is accomplished by means of the sprocket 24, fixed on the extension 19 of the tube between'the bearing 20 and the gland 21, and a chain 25 driven by a suitable source of power (not shown).

Surrounding the tube 18 is a stationary tubular shell 28. The shell 28 is provided with extensions 29 and 30 which, respectively, project through the end walls 32 and 33 of a heating chamber 31 within which the still 17 is located. Glands 34 and 35 surrounding, respectively, the shaft 22 and the tube extension 19 provide seals at the points of exit thereof. At spacedintervals within the chamber 31 the shell 28 rests on and is supported by rollers 38 carried on tables 39. The base of each of the latter is enclosed in insulating material 40. The rollers 38 not only furnish support for the shell 28 but also facilitate longitudinal expansion and contraction of the shell with changes in' temperature.

The tube 18 is provided'interiorly with a plurality of angularly disposed, longitudinally and circumferentially spaced plates or vanes 43. Similar, but oppositely inclined vanes 44 are also longitudinally and circumferentially spaced on the exterior of the tube 18. Adjacent its closed end, the tube 18 is provided with circumferentially spaced ports 45 and the vanes 43 and 44 are so disposed that, upon rotation of the tube, metal powder fed into the tube by the conveyor 8 will be transported by vanes 43 through the interior of the tube to the ports 45, will drop through ports 45 from the tube into the shell 28, and will then be transported in the reverse direction by vanes 44 to the chute 46 at the other end of the shell 28. The chute 46 communicates with and feeds into a screw conveyor 47, preferably mounted normal to the axis of the still 17, that carries the metal powder to a point outside the heating chamber 31.

A burner, the nozzle 51 of which extends into the heating chamber 31, provides heat for the still 17 and the hot combustible gases therefrom pass into the fiue 4 which communicates with the interior of the chamber 31 through the top 52 thereof. The combustion gases after rising through the column 3 are passed through a scrubber which, as shown, may comprise a tank 53 packed with granular, porous material such as coke 54 which is cooled and kept wet by water sprays from the pipe 55. An outlet or stack 56 is provided for the scrubbed gases, and the water and recovered material is withdrawn through the drain 57.

Volatile matter evolved from the metal powder in the still is carried out through the duct 60 and may be led to a condenser (not shown) or any other desired apparatus. If feasible, so far as pollution of the atmosphere is concerned, the duct 60 can merely exhaust to the air. Gas to assist in carrying off evolved volatile matter through the duct 60 is preheated by passing it through a pipe 61 into a heating shell 62 that surrounds the conveyor 47. From the shell 62 the hot gas passes through the connection 63 into the conveyor counter current to the movement of metal powder and then into the shell 28 of the still.

In carrying out the process of the present invention with the apparatus described above, the contaminated metal powder is fed by the conveyor 1 to the feed tube 2. The grid 6 breaks up lumps and the powder drops through the column 3 in dispersed condition counter current to the flow of hot gases from the flue 4. Column 3 should be of sufiicient diameter as to prevent such flow rates of the hot gases as will carry out any of the metal powder. The hot gases, which are preferably at a temperature of about 700 F., heat the metal particles, evaporating water from the surfaces and vaporizing a portion of the organic contaminants thereon, thus minimizing caking and agglomeration of the particles during subsequent treatment.

From the collector at the lower end of the column 3 the preheated metal powder is carried by the screw conveyor 8 into the rotating tube 18 of the still where the powder is further heated to increasingly higher temperatures as it is pushed by the plates or vanes 43 to the closed end of the tube and then pushed back along the bottom of the shell 28 by the vanes 44. In this second stage of heating, during which the metal powders preferably reach a temperature of at least 1000" F. and may be heated to about 1600 F., substantially all of the organic contaminants are decomposed and/or vaporized.

Heating of the metal powder in the still 17 is brought about by heat supplied from the burner, the nozzle 51 of which opens into the heating chamber 31 and also by heat supplied by gas entering the still through the chute 46 after being heated by passage around and through the conveyor 47. As will be evident, the metal powder from the still transported by the conveyor 47 is concurrently cooled. After leaving the conveyor the metal powder is further cooled and is then ready for use or further treatment if desired.

When the metal powder has been produced by grinding operations there will be mixed with it particles of the grinding wheels used. In some cases it will be desirable to separate these non-metallic particles. If the metal powder is ferromagnetic, magnetic separation can be employed. In other cases, other known and suitable methods, such for example as electrostatic separation, may be used. Any carbon deposits left on the metal powder as a result of decomposition of organic matter can be substantially removed by air-blowing because of the lower specific gravity of the carbon. If desired milling may be employed to loosen the carbon.

As mentioned above, it is preferred to heat the metal powder during the first heating stage to about 700 F. However, the exact temperature used will depend largely upon the temperature of the combustion gases introduced into column 3 through the flue 4. In the second heating stage, for ferrous metal powders a temperature of from 1000 F. to 1600 F. is preferred. Of course, metal powders which are heat sensitive or have low melting points may necessitate the use of lower temperatures in one or both stages of heating.

Heating of the still 17 may be accomplished by use in the burner indicated of oil, gas or powdered coal. Also, of course, other suitable heating methods may be used. The firing may be so regulated as to vary the combustion gases passing through the flue 4 and column 3 from oxidizing to reducing. It is preferred, however, for these gases to be non-oxidizing and at least slightly reducing in nature. The gas introduced into the still 17 through the chute 46 is also preferably reducing and may be derived from any desired source. Examples of useful gases are natural gas, flue gas, and dissociated ammonia. By use of a reducing atmosphere in the still oxidation of the metal particles is prevented and in some cases oxides are reduced to metal. The still may be operated with either a positive or a reduced pressure therein by means of Well known expedients.

Any suitable materials may be employed in constructing apparatus for carrying out the novel process of the present'invention although in general steel is preferred from the standpoint of expense. Where relatively high temperatures will be encountered, chrome or other suitable heat resistant alloy steels may be employed. The heating chamber 31 is preferably formed of suitable heat-resistant ceramic material such as fire brick or the like and suitable insulating or heat-resistant coverings 40 are provided for the posts or bases of the roller supporting tables 39. As previously pointed out, it is prefe'rred'to provide insulation on the exteriors of the flue 4 and the duct 60 to prevent undesirable cooling of the gases and vapors therein.

It will be understood that the present invention is not limited to the recovery of metal powder from grinding residues, but may be used for the purification of metal powders contaminated with oils and other organic materials from any source. While primarily useful with finely divided metal the present process is also adapted for the purification of granular metal chips, flakes, shot, etc., resulting from various metallurgical and metal working processes which may be contaminated as described. As is'evident, the process is simple and inexpensive while, at the same time, eflicient.

It will also be understood that numerous variations and modifications can be made in the apparatus shown and described within the scope of the invention. As examples of such variations and modifications, the following are mentioned: The vanes 43 and 44 may be of any desired size and shape and may be located as necessary to provide the desired agitation and movement of the metal powder in the still. If desired, instead of vanes, the rotary tube 18 may be provided with one or more spiral ribbons on the inside, the outside, or both, which are so arranged as to agitate and propel the metal powder through the still. In place of the grid 6, other known devices may be employed in the column 3 to break up aggregates of metal powder and disperse the powder in the column. Also, of course, the rotating tube 18 may be supported and/or driven in other ways and, as previously mentioned, the still may be heated by other means.

It is, therefore, intended that the present invention shall not be interpreted narrowly, but shall be construed as broadly as is permitted by the appended claims.

I claim:

1. A process for removing organic contaminants from metal powder which comprises heating said metal powder in a first heating zone by a current of hot gas while said powder is dispersed in said gas, collecting said powder and feeding it to a second heating zone, mechanically agitating said powder in said second heating zone while heating said powder, in a reducing atmosphere, to a temperature higher than that in said first heating zone.

6 2. A process as set forth in claim 1 in which the hot heating zone and to a temperature of from 1000 F. to gas in said first heating zone is non-oxidizing. 1600 F. in said second heating zone.

3. A process as set forth in claim 1 in which reducing gas is introduced into said second heating zone and car- References Clted m the file of thls patent ries away vaporized contaminants. 5 UNITED STATES PATENTS 4. A process as set forth in claim 2 in which said 2,158,689 Buchanan May 16, 1939 powder is heated to at least about 700 F. in said first 2,296,422 Carl Sept. 22, 1942 heating zone and to a temperature of from 1000 F. to 2,368,282 Wulfi Jan. 30, 1945 1600 F. in said second heating zone. 2,688,575 Banuss et a1. Sept. 7, 1954 5. A process as set forth in claim 3 in which said 10 2,666,714 Halberstadt Jan. 19, 1954 powder is heated to at least about 700 F. in said first 2,798,018 Derge July 2, 1957 

1. A PROCESS FOR REMOVING ORGANIC CONTAMINANTS FROM METAL POWDER WHICH COMPRISES HEATING SAID METAL POWDER IN A FIRST HEATING ZONE BY A CURRENT OF HOT GAS WHILE SAID POWDER IS DISPERSED IN SAID GAS, COLLECTING SAID POWDER AND FEEDING IT TO A SECOND HEATING ZONE, MECHANICALLY AGITATING SAID POWDER IN SAID SECOND HEATING ZONE WHILE HEATING SAID POWDER, IN A REDUCING ATMOSPHERE, TO A TEMPERATURE HIGHER THAN THAT IN SAID FIRST HEATING ZONE. 